The power converter employed for controlling the electric motor of the railway vehicle and the large-sized industrial apparatus, and for the large-capacity frequency converter of the electric power system is configured to execute large-current power control at high voltage. Upon occurrence of failure in operation, the aforementioned device may cause damage to the system, and unplanned system down, resulting in possible serious economic loss. In order to prevent the aforementioned circumstances, it is necessary to prevent destruction owing to the function stop, notify relevant parties of necessity of the maintenance work, and execute the life extending control of the power converter for suppressing deterioration by detecting deterioration and abnormality before destruction occurs.
For example, there is the method of detecting over-temperature abnormality of the power converter detected by the temperature sensor disposed near the power semiconductor for conduction-interruption of the current. However, it is difficult for such power converter to detect temperature rise of the semiconductor chip owing to the thermal resistance increase in the power semiconductor. Accordingly, direct detection of the temperature abnormality of the semiconductor chip by itself is demanded as disclosed in Japanese Unexamined Patent Application Publication No. Hei 7-170724 (Patent Literature 1). In the aforementioned example, the control command signal and the delay time elapsing until interruption of the power semiconductor are detected so that the temperature rise in the power bipolar transistor is detected.
Japanese Unexamined Patent Application Publication No. 2000-324846 (Patent Literature 2) discloses the method of detecting current abnormality of the element. The power converter including an inductance connected to a main terminal of the switching element, and an integrator for integration of the voltage generated at both ends of the inductance is used so that the output current of the switching element is obtained. If the obtained output current value exceeds the specified value, the switching element is interrupted for preventing destruction of the element.